This invention relates to an acoustical energy transfer component for any of a variety of applications to transfer input acoustical energy to an output location.
Acoustical energy transfer components are used in a wide variety of applications such as, but not limited to, radar, ultrasonic cleaning, waveguides, ultrasonic bonding, ultrasonic perforating, and ultrasonic cutting. Among examples are an ultrasonic horn, booster, and converter used in bonding two thermoplastic sheets of material together in the manufacture of personal care products such as diapers. Another example is an acoustic biosensor for deployment at an implantation site. Another example is a piezoelectric acoustic component used as a piezoelectric buzzer or a piezoelectric receiver that generates an alarm sound or an operating sound in electronic equipment, household electrical appliances, or mobile telephones. Another example is apparatus for acoustic pressure assisted wave soldering of components onto printed circuit boards. Another example is an ultrasonic endoscope.
Upon energization acoustic energy transfer components cyclically expand and contract. For example, an ultrasonic horn for bonding may expand and contract a total amplitude of 0.003 inches (0.0075 cms) at a frequency of 20,000 Hz. This translates to a total movement of 120 inches (300 cms) of movement per second. This movement corresponds to an energy value applied to the work piece. Some of the energy is simply returned as elastic reaction, and most of the energy is dissipated as heat, which melts the two materials being bonded.
Generally, acoustical energy transfer components have been manufactured by machining a final component shape from forged bar stock, such as titanium bar stock. Forging by its nature mechanically deforms grains, yielding a wrought microstructure. The alignment of deformed grains according to a wrought microstructure affects the natural cyclic bulk expansion and contraction of the component as it is energized. In particular, the natural expansion and contraction is orthotropic or non-isotropic, that is, it is not uniform in all directions, and is preferential in one or more directions. The expansion and contraction in various directions is affected by the directional alignment of grains in the microstructure.
Inasmuch as a forged component expands and contracts non-uniformly, the degree of expansion and contraction in a given direction varies slightly depending on how the grains are aligned with respect to the component. As such, there are directions of maximum expansion and contraction, directions of minimum expansion and contraction, and directions of intermediate expansion and contraction. This type of non-uniform acoustical behavior can be undesirable. With ultrasonic rotary horns for bonding, for example, the horn is continually rotating, such that some products are bonded with the horn in a rotary position of maximum expansion and contraction, other products are bonded with the horn in a rotary position of minimum expansion and contraction, and other products are bonded with the horn in a rotary position of intermediate expansion and contraction. The amount of energy transferred to respective work pieces therefore varies, and non-uniform bonding or other work can result.
For many acoustical energy transfer components, resonant operating frequency is a critical parameter. In particular, for a given application such as radar, cleaning, or ultrasonic bonding, efficient operation requires that the component resonate at a predetermined, known frequency. With a horn, for example, this resonant operating frequency is largely dependent on the outside diameter of the horn. As a general proposition, as the size of the component is reduced, in many applications, the resonant frequency increases. However, not all forged components of the same size have the same resonant operating frequency, because resonant operating frequency is also largely dependent on the microstructure of the component. And because wrought microstructures vary substantially in terms of grain size and grain alignment from one forging to the next, there is a corresponding variance from one forging to the next in terms of resonant operating frequency, even for forgings of the same size. As such, just because a first forging of a given size is determined to have a resonant operating frequency of 20,000 Hz does not mean that a second forging of the same size will also have a resonant operating frequency of 20,000 Hz. This is especially true of forgings from distinct billets having distinct microstructures. Each forging must be separately tuned to the desired frequency. In order to tune a component to, for example, 20,000 Hz, the practice has been to produce the component slightly oversized and then machine the component progressively smaller until the frequency of 20,000 Hz is achieved.
In response to the above difficulties and problems, the invention provides an acoustical energy transfer component which has isotropic expansion and contraction characteristics upon acoustical excitation. The invention also provides an acoustical energy transfer component for which the need for tuning is substantially reduced or eliminated.
Briefly, therefore, the invention is directed to an acoustical energy transfer component for transporting acoustical energy comprising a shaped metal component body having a substantially uniformly isotropic expansion and contraction amplitude upon acoustical excitation.
The invention is also directed to a method for manufacturing an acoustical energy transfer component for transporting acoustical energy. The method comprises mechanically pressing metal powder into a component body preform; and hot isostatically pressing the component body preform to consolidate the metal powder to form a shaped metal component body having a uniform isotropic microstructure characterized by randomly isotropic directional grain alignment such that the component body has a uniformly isotropic expansion and contraction amplitude upon acoustical excitation.
Other features and advantages will be in part apparent and in part pointed out hereinafter.